Continuous stream ink jet printing uses a pressurized ink source which produces a continuous stream of ink droplets. Stimulation devices, such as heaters positioned around the nozzle, stimulate the stream to break up into drops with either relatively large volumes or relatively small volumes. These drops are then directed by one of several means, including electrostatic deflection or gas flow deflection. Printheads utilizing gas flow for deflection are known and have been described.
In one form of such printheads, the drop deflecting gas flow is produced at least in part by a gas, typically air, drawn into a negative air duct as a result of vacuum applied to the duct. Drops of a predetermined small volume are deflected more than drops of a predetermined large volume. This allows for the small drops to be deflected into an ink capturing mechanism (catcher, interceptor, gutter, etc.) where they are either recycled or discarded. The large drops are allowed to strike the print medium. Alternatively, the small drops may be allowed to strike the print medium while the larger drops are collected in the ink capturing mechanism.
It has been determined that while small drops are deflected by the lateral airflow more than large drops, not all small drops follow the same trajectory. Some of these drops can be deflected sufficiently by the air flow such that they enter the gas flow duct, causing ink puddles to form. Ink puddles in the air duct can also be formed during startup and shutdown of the printhead caused by ink dripping off the upper wall of the gas flow duct and landing on the lower wall of the gas flow duct. Additionally, ink puddles can be formed due to a crooked jet which causes ink to be directed into the gas flow duct. Ink from the puddles of ink in the gas flow duct can be dragged by the gas flow up into the vacuum source that is attached to the gas flow duct, potentially damaging the vacuum source. If the ink puddles remain close to the entrance to the duct, these puddles can affect the uniformity of the air flow across the width of the jet array. Ink puddles can induce oscillations in the gas flow that can produce a modulation in the print drop trajectories that adversely affect print quality.
Accordingly, a need exists to maintain the cleanliness of the gas flow duct and remove ink puddles formed therein.